Japanese authorities said Sunday that efforts to restart the cooling system at one of the reactors damaged by Friday's earthquake had failed, a major setback in the struggle to contain what has become the most serious nuclear power crisis in a quarter century.

The secretive disinformation campaign sought to undermine Hillary Clinton, bolster Donald Trump and turn Americans against each other. The accounts of some former Russian trolls ? along with details from the indictment against the Internet Research Agency and 13 Russian associates ? underscore the sophistication and ambition of the program.

Special counsel Robert Mueller ultimately might conclude that there was no clear case of collusion between the Russians and associates of President Trump?s 2016 campaign. But he has laid down a challenge to the president that no longer can be ignored.